When reading and writing to a variety of locations on a mechanical hard disk drive, there are often latencies involved due to the seek time required for a hard disk drive head to move from place to place on a disk. However, flash memory is a solid state recording mechanism with no moving parts, and thus has a faster read access time than a mechanical hard drive. This is because reading from a flash drive does not suffer from latency due to head-seek time, as typically will be the case with a mechanical hard drive. Because of this, reading from a flash drive can be more than ten times faster than reading from a mechanical drive. This improved read speed is one reason that flash drives are replacing mechanical hard disk drives in many computing uses.
Memory space in typical flash drives is organized in regions or arrays called cells. A limitation of flash memory is that, while it can be randomly read and written, it can only be block erased or cleared. A cell in a flash drive can physically wear out over time after some finite number of clear operations is performed on the cell as part of the writing/re-writing process. Typically the number of clear operation cycles required to wear out a cell is in the range of around 100,000 to 1,000,000 clear operations.
Typically, when data in a cell needs to be re-written, the old data is marked as invalid and the replacement data is written to an available area in the cell. When no more room is available in the cell, the cell is block cleared and new data is then written to the cleared cell along with valid data that was copied out of the cell before it was cleared. This clearing frees up the previously invalid portions of the cell to be written to again. This process for writing data in a flash drive is but one technique of “wear leveling” employed in flash drives in an endeavor to limit the number of clearing operations performed to a cell.
As flash drives are becoming larger and more common they are being used more and more as supplemental storage and also as primary storage media in place of mechanical disk drives. Because of this increased reliance on flash drives, use with certain programs and/or applications will cause cells in a flash drive to be overstressed. This will result in a shortened life span for the flash drive, in spite of the employment of current wear-leveling techniques. A shortened lifespan is not desirable, particularly when a flash memory is used as primary storage.
Thus, a technology which addresses some of the above disadvantages and shortcomings of flash drives would be advantageous.